1. Field of the Invention
This invention relates to a hydraulic tensioner for imparting a proper tension to a traveling chain, belt or the like, and particularly to a hydraulic tensioner in which the dropping-out of a metallic cylinder fitted into a cylindrical hole formed in the body of the tensioner is prevented by use of a compression spring provided so as to protrude the tip of a plunger from the body without fixing the cylinder by a separate fixing member or the like.
2. Description of the Prior Art
FIG. 6 shows a conventional hydraulic tensioner 51 as an example. This hydraulic tensioner 51 comprises an iron-based plunger 54 slidably fitted into a cylinder chamber 53 formed in an iron-made or aluminum alloy-made body 52.
A hollow part 55 opened at the lower end is formed within the plunger 54, and a compression spring 56 for energizing the plunger 54 to impart a proper tension to a chain, belt or the like (not shown) is housed in the hollow part 55. A pressure oil chamber 57 is formed by the hollow part 55 and the cylinder chamber 53 of the body 52, and a check valve 58 allowing the inflow of oil to the pressure oil chamber 57 but arresting the back flow thereof is provided on the bottom of the pressure oil chamber 57.
The check valve 58 is formed of a ball seat 59 pressed into a cylindrical hole 63 in the lower part of the pressure oil chamber 57, a check ball 61 provided on the upper part of the through-hole 60 of the ball seat 59, a coil spring for energizing the check ball 61 toward the through-hole 60, and a retainer 62 for supporting the end of the coil spring, and the check ball 61 functions as check valve.
The pressure oil chamber 57 is regularly filled with the oil externally supplied from an inlet port 64 and the through-hole 60 by a pump or the like through the check valve 58. When the traveling chain, belt or the like gets loose, the plunger 54 regularly energized by the compression spring 56 is protruded, and the check valve 58 is opened to allow the oil to flow into the pressure oil chamber 57. When the plunger 54 is pushed into the cylinder chamber 53 by an impact force worked from the chain, belt or the like to the tensioner, the oil pressure in the pressure oil chamber 57 is raised to close the check valve 58.
When the check valve 58 is closed, the oil in the pressure oil chamber 57 is released from the lower end of the plunger 54 through a clearance (slight space) between the outer surface of the plunger 54 and the inside surface of the cylinder chamber 53 and discharged to the outside. At this time, the impact energy is absorbed by the flowing resistance of the oil passing through the clearance, and a cushion effect can be obtained.
However, since the body 52 consists of a die cast product of cast iron or aluminum alloy, the conventional hydraulic tensioner 51 has the problem of requiring film formation by coating, smoothing treatment, machining or the like to ensure the surface precision or durability of the cylinder chamber for sliding the plunger for the purpose of preventing the wear and seizure of the plunger. Further, it requires an improvement in precision of the cylindrical hole 63 since the ball seat 59 constituting the check valve 58 is pressed into the cylindrical hole 63 formed in the lower part of the pressure oil chamber 57, which causes the problem of requiring the machining therefor.
When the surface precision and durability of the cylinder chamber is inferior as described above, it is also proposed to clearance-fit a metallic cylinder of separate part into the cylindrical hole formed in the body (Japanese Patent Application Laid-Open No. 2000-346152). In this case, however, it is necessary to form an annular recessed groove on the inside surface of the cylindrical hole and mount a snap ring on the recessed groove for the prevention of dropping-out of the cylinder, resulting in the necessity of processes for groove formation, snap ring mounting and the like, which increases the manufacturing cost for this portion.
Since the body consisting of the die cast product of cast iron, aluminum alloy or the like is heavyweight, it is also considered to make the body of plastics in order to reduce the weight. However, the insert molding of a reinforcing part such as metallic cylinder or the like is required because of the presence of problems such as insufficient durability of the sliding surface with the plunger, insufficient strength of each part or the like, causing the problem of complicating a metal mold to increase the cost. Further, a looseness is caused in a temperature rise by the difference in thermal expansion coefficient with a press-in member such as the ball seat of the check valve, so that high-pressure oil cannot be supplied to the pressure oil chamber.
In order to solve the problems of the prior arts as described above, this invention has objects to facilitate the mounting of a cylinder and the assembling of a tensioner by dispensing with the film formation, smoothing treatment, machining or the like of a cylinder chamber for sliding a plunger on the body of the tensioner and also dispensing with machining of hole surface or the like in the fitting of the metallic cylinder of separate article, and to prevent the dropping-out of the cylinder by use of a compression spring provided so as to protrude the plunger from the body without requiring any cylinder fastener such as snap ring of separate member. Further, it has objects to prevent also the dropping-out of a check valve mechanism by use of the bottom plate of the cylinder in the mounting of the check valve mechanism and to facilitate the assembling thereof.
In order to attain the above objects, a hydraulic tensioner according to a first aspect of this invention comprises a metallic cylinder fitted to a cylindrical hole formed in a body, a plunger provided within the cylinder so as to be energized by a compression spring to protrude the tip from the body, and a pressure oil chamber formed between the inner part of the plunger and the cylinder, wherein the cylinder is provided with a bottom plate having a through-hole allowing the inflow of oil in the center, and the bottom plate is prevented from dropping out from the body by being energized by the compression spring.
According to a second aspect of this invention, in the hydraulic tensioner of the first aspect, the cylindrical hole is provided with a cylindrical hole smaller in diameter than this cylindrical hole on the bottom side, and a check valve mechanism fitted to the minor diameter cylindrical hole is prevented from dropping out by the abutment on the bottom plate of the cylinder.
According to a third aspect of this invention, a hydraulic tensioner comprising a metallic cylinder fitted to a cylindrical hole formed in a body, a plunger provided within the cylinder so as to be energized by a compression spring to protrude the tip from the body, a pressure oil chamber formed between the inner part of the plunger and the cylinder, and a check valve mechanism allowing the inflow of oil to the pressure oil chamber but arresting the back flow thereof, wherein the cylinder is provided with a bottom plate having a through hole allowing the inflow of oil in the center, and the bottom plate being prevented from dropping out from the body by being energized by the compression spring, the check valve mechanism comprises a check ball provided so as to block an inflow hole of oil to the pressure oil chamber from above and a spring for energizing the check ball and the spring is supported by the bottom plate, is provided.
Further, according to a fourth aspect of this invention, a hydraulic tensioner according to the third aspect, wherein the check valve mechanism further comprises a lid for supporting the spring and being a preliminary assembled product, and the lid is supported by the bottom plate, is provided.
A hydraulic tensioner according to a fifth aspect of this invention comprises a metallic cylinder fitted to a cylindrical hole formed in a body, a plunger provided within the cylinder so as to be energized by a compression spring to protrude the tip from the body, a pressure oil chamber formed between the inner part of the plunger and the cylinder, and a check valve mechanism allowing the inflow of oil to the pressure oil chamber but arresting the back flow thereof, wherein the cylinder is provided with a bottom plate having a through-hole allowing the inflow of oil in the center, the bottom plate is prevented from dropping out from the body by being energized by the compression spring through the retainer of the check valve mechanism, and the check valve mechanism comprises a check ball provided so as to block the through-hole formed in the bottom plate from above, a spring for energizing the check ball, and the retainer for supporting the spring.
According to a sixth aspect of this invention, in a hydraulic tensioner according to any one of the preceding aspects, a ratchet pawl body to be engaged with a ratchet tooth engraved in the outside surface of the plunger is rockably provided on the body by spring energization in order to prevent the backward displacement of the plunger, a cutout for rocking the ratchet pawl body engageably with the ratchet tooth and a pair of protruding pieces extending outward from the end of the cutout are formed on the cylinder, and the ratchet pawl body is supported through a shaft inserted to mount holes formed in the protruding pieces and a mount hole formed in the body.
According to a seventh aspect of this invention, a hydraulic tensioner according to any one of the preceding aspects, wherein the body is made by die-casting and the cylinder is made of steel iron, is provided.
Moreover, according to an eighth aspect of this invention, a hydraulic tensioner according to any one of the preceding aspects, wherein the body is made by synthetic resin molding and the cylinder is made of steel iron.
In this invention, the body may consist of a die cast product of cast iron, aluminum, aluminum alloy, a plastic product or the like without specially limiting the material thereof. As the cylinder, any metallic cylinder of steel iron, cast iron, sintered metal or the like can be used if it never causes a seizure with the plunger without specially limiting the material thereof.
When the hydraulic tensioner of this invention is mounted on an engine, a drive unit or the like, the compression spring energizes the bottom plate of the cylinder since the plunger provided so as to protrude the tip from the body of the tensioner is pressed by a chain, belt or the like and pushed so as to retreat into the cylinder, and the dropping-out of the cylinder can be thus prevented without separately providing any fastener. The thus-prevention of dropping-out of the bottom plate of the cylinder by the compression spring allows the clearance fit of the cylinder. When the die cast product of cast iron, aluminum, aluminum alloy or the like or the plastic product by synthetic resin molding is used as the body, the cylindrical hole for fitting the cylinder requires no surface treatment, machining or the like, and the surface treatment, machining or the like of the mounting surface to the engine, drive unit or the like is also dispensed with in the use of the plastic product.